Many electronic devices, such as conventional computing devices now include graphics subsystems capable of rendering two and three dimensional graphics; decoding and encoding motion video; and the like. To provide these features and desired processing speeds, modern graphics subsystems include an ever increasing number of transistors. Not surprisingly, the increase in transistor counts has led to corresponding higher electric power consumption by the graphics subsystems.
As a consequence, the fastest and feature-rich graphics subsystems have, for the most part, been reserved for devices that can meet the increased power demands. Portable computing devices, such as laptops, personal digital assistants, video and audio players, cellular telephones, and the like have often been equipped with functionally limited, but electrically efficient (i.e. lower power) components.
Often these graphics subsystems are integrated in other computing components such as processor interconnect circuits (often referred to as “chipsets”).
Recently, there has been a trend to provide graphics features and performance that rival those of stationary computers for portable devices. Often, this is done by allowing the addition of an optional, external high power graphics subsystem to portable devices. The PCI express (PCIe) standards, for example, contemplates interconnection of PCI express compliant graphics cards, including a graphics subsystem, as external components to laptop computing devices.
At the same time, advances in other computing features, such as wireless components, large displays, and the like, have created demand for longer battery life to power portable devices and notebook computers.
One way of extending battery life is to temporarily reduce the power consumed. The total amount of power that a device consumes is determined by the individual power demands of device components. For example, the central processing unit (CPU), hard disk drive (HDD), and graphics subsystem all have individual power demands.
Accordingly, power reduction techniques include clock gating, voltage throttling, and resource hibernation. Clock gating reduces consumed power by reducing transistor and capacitor switching activity. This is accomplished by allowing a circuit in an electronic device to control whether or not, and at what speed, the clock signal reaches idle circuits in the processor.
Voltage throttling reduces overall power consumption by lowering the supply voltage to a processor in an electronic device. Supply voltage reductions are generally done in tandem with reductions in clock frequencies.
Resource hibernation allows particular components of an electronic component to be powered down, placed into a “sleep mode”, or otherwise placed in a lower power consumption mode during periods of inactivity. The Advanced Configuration and Power Interface (ACPI) specification, for example, defines a number of different device power states that may be combined to reduce the overall power consumed.
Optimizing the balance between delivering high performance and conserving battery life continues to present challenges. Accordingly, there remains a need for methods and apparatus that lower the power consumption associated with graphics processing in electronic devices and computers.